Electric discharge device



June 26, 1928,

C. V. FERGUSON ELEO'PRIC HDISCHARGE I'm-VICE ,mea Dec. 15, 1925.

l l l l l l l l l J- J 4 g Inventor? I clwia rl e s V. Fe r-guson His Attorney.

Patented June 26, 1928.

UNITED STATES PATENT OFFICE.

CHARLES V. FERGUSON, OF SCHENECTADY, NEW YORK, ASSIGN OR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC DISCHARGE DEVICE,

The present invention relates to construction of cathodes for electrical discharge devices, and in particular to cathodes for devices in which the cathode constitutes the seat of an arc-like discharge, as, for example,

in a hot cathode rectifier.

It is the object of my invention to provide a rugged cathode suitable for relatively high current'operation.

In thermionic gaseous discharge devices of the type described in Meikle Patent, No. 1,182,290 of May 9, 1916, the seat of the arelike discharge is an incandescent filament which is commonly heated during operation by its electrical resistance to a current traversing the same during operation. This cathode construction and mode of heating the cathode is one of the features limitingthe permissible current carrying capacity of the device and introduces structural difliculties.

In accordance with my present invention, I have provided a cathode comprisingmembers of concentrated mass which make an imperfect contact with one another, so that these masses may be heated at the region of high transition resistance by a current which is not too excessive to be conveyed by ordinary sealed-in conductors.

The accompanying drawings show in Fig. 1 a rectifier containing a cathode embodying my in ention; Fig. 2 is an enlarged view of the cathode, and Figs. 3 and .4 illustrate modifications. I

The rectifier shown in Fig. 1 comprises a glass envelope '1, containing a suitable gas, for example, argon, and being provided with an anode 2, and a cathode 3, joined respectively to leading-in conductors 4, 5 and 6, which are sealed into the glass envelope in the usual way. The anode may consist of carbon or a suitable refractory metal, such as molybdenum or tungsten. The cathode conductors 5, 6 are joined to the contacts 7 8 of an external screw base. A heating current is conveyed thereto by the conductors 9, 10, from any suitable source, as for example, a portion of the secondary of an auto-transformer, 11, which also serves to charge the battery 12 through the conductors 13, 14.

As best shown in Fig.2, the cathode comprises cylindrical discs, or buttons 15, 16,

which are respectively attached to the conductors 5, 6, by the stems 17, 18 which have a smaller diameter than the discs to prevent undue loss of heat by conduction. The latter are in contact at their edges. As this contact has a high transition resistance, less current is required to generate suflicient heat at the point of contact to raise the members 15, 16, to incandescence than would be re quired otherwise.- The masses whichare in imperfect contact may assume various shapes. 4 V

Fig. 3 illustrates a cathode having a pointed or cone-shaped member 19 contacting at its tip with a disc-shaped member 20, and Fig. 4 illustrates another modification comprising wedge-shaped members 21, 22, making an edge to edge contact. In the modification shown in Fig. 3', the stems 28, 24 are elongated and have a right-angled bend whereas the stems 25, 26 of Fig. 4 are short and straight, being joined by welding across the top of the conductors 5, 6. In some cases, especially when relatively long thin stems are used the contacting cathode mem bers are pressed into contact lightly by the springiness of the stems.

:Contrary to what might be expected, the arc does not concentrate during operation at the hottest portion of the cathode, that is, at the high resistance contact, and there cause local disintegration, but emanates as a diflused glow from the entire heated surface. The cathode therefore, has a commercially long life. Because of its exceedingly simple structure, my improved cathode is easily and cheaply constructed.

What I claim as new and desire to secure by Letters Patent of the United States, is

A cathode for an electrical discharge device, said cathode comprising button-shaped members of concentrated mass and supports therefor of lesser cross section than said members and constructed to hold said members in high resistance contact with each 7' 

